1. Field of the Invention
The present invention relates to a solder alloy used as a bonding material for mounting electronic parts on a printed circuit board (PCB), and more particularly, to a tin-silver-copper group (Sn—Ag—Cu group) solder alloy having no lead (Pb) component.
2. Description of the Related Art
Solder is used to mount electronic parts such as semiconductor chips or discrete components on a PCB. The most common solder composition is a binary alloy of Sn and Pb. However, Pb is harmful to the human body, and eventually pollutes the environment. Thus, the use of Pb in the manufacture of a solder alloy is now regulated or excluded in the electronic industry, to encourage the development of an environmentally friendly Pb-free solder alloy. A ternary Pb-free solder alloy of Sn—Ag—Cu has been suggested as the best candidate to replace the binary solder alloy of Sn—Pb.
However, the ternary Pb-free solder alloy of Sn—Ag—Cu oxidizes more easily than the binary solder alloy of Sn—Pb. Thus, an excessive amount of dross is generated, bond strength is reduced, and the flow and wetting properties are deteriorated. Also, the ternary Pb-free solder alloy of Sn—Ag—Cu is sensitive to impact, and is thus unsuitable for portable appliances such as cellular phones, digital cameras, and the like.
Thus, attempts have been made to add phosphor (P), gallium (Ga), or the like to the ternary Pb-free solder alloy of Sn—Ag—Cu, to prevent dross or oxidation. Although this successfully prevents oxidation, the resulting alloy is brittle and thus weak to impact. It is therefore difficult to use the ternary Pb-free solder alloy of Sn—Ag—Cu in portable appliances.